On this Wikipedia ninja blender for crushing ice language links are at the top of the page across from the article title. Drawing of the archetypical ninja from a series of sketches by Hokusai.

In the unrest of the Sengoku period, mercenaries and spies for hire became active in Iga Province and the adjacent area around the village of Kōga. It is from these areas that much of the knowledge regarding the ninja is drawn. Ninja figured prominently in legend and folklore, where they were associated with legendary abilities such as invisibility, walking on water and control over natural elements. The word shinobi appears in the written record as far back as the late 8th century in poems in the Man’yōshū.

Historically, the word ninja was not in common use, and a variety of regional colloquialisms evolved to describe what would later be dubbed ninja. In fiction written in the modern era kunoichi means “female ninja”. World War II culture, possibly because it was more comfortable for Western speakers. Despite many popular folktales, historical accounts of the ninja are scarce. Historian Stephen Turnbull asserts that the ninja were mostly recruited from the lower class, and therefore little literary interest was taken in them. So-called ninjutsu techniques, in short are the skills of shinobi-no-jutsu and shinobijutsu, which have the aims of ensuring that one’s opponent does not know of one’s existence, and for which there was special training.

However, some ninjutsu books described specifically what tactics ninja should use to fight, and the scenarios a ninja might find themselves can be deduced from those tactics. Yamato Takeru dressed as a maidservant, preparing to kill the Kumaso leaders. The title ninja has sometimes been attributed retrospectively to the semi-legendary 4th-century prince Yamato Takeru. It was not until the 15th century that spies were specially trained for their purpose. It was around this time that the word shinobi appeared to define and clearly identify ninja as a secretive group of agents. Amongst the samurai, a sense of ritual and decorum was observed, where one was expected to fight or duel openly.